* tsh – A tiny shell program with job control
*
#include
#include
#include
#include
#include
#include
#include
#include
#include
/* Misc manifest constants */
#define MAXLINE 1024 /* max line size */
#define MAXARGS 128 /* max args on a command line */
#define MAXJOBS 16 /* max jobs at any point in time */
#define MAXJID 1<<16 /* max job ID */
/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1 /* running in foreground */
#define BG 2 /* running in background */
#define ST 3 /* stopped */
* Jobs states: FG (foreground), BG (background), ST (stopped)
* Job state transitions and enabling actions:
* FG -> ST : ctrl-z
* ST -> FG : fg command
* ST -> BG : bg command
* BG -> FG : fg command
* At most 1 job can be in the FG state.
/* Global variables */
extern char **environ; /* defined in libc */
char prompt[] = “tsh> “; /* command line prompt (DO NOT CHANGE) */
int verbose = 0; /* if true, print additional output */
int nextjid = 1; /* next job ID to allocate */
char sbuf[MAXLINE]; /* for composing sprintf messages */
char * username; /* The name of the user currently logged into the shell */
struct job_t { /* The job struct */
pid_t pid; /* job PID */
int jid; /* job ID [1, 2, …] */
int state; /* UNDEF, BG, FG, or ST */
char cmdline[MAXLINE]; /* command line */
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */
/* Function prototypes */
/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);
void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);
/* Here are helper routines that we’ve provided for you */
int parseline(const char *cmdline, char **argv);
void sigquit_handler(int sig);
void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs);
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid);
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid);
int pid2jid(pid_t pid);
void listjobs(struct job_t *jobs);
char * login();
void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);
* main – The shell’s main routine
int main(int argc, char **argv)
char cmdline[MAXLINE];
int emit_prompt = 1; /* emit prompt (default) */
/* Redirect stderr to stdout (so that driver will get all output
* on the pipe connected to stdout) */
dup2(1, 2);
/* Parse the command line */
while ((c = getopt(argc, argv, “hvp”)) != EOF) {
switch (c) {
case ‘h’: /* print help message */
case ‘v’: /* emit additional diagnostic info */
verbose = 1;
case ‘p’: /* don’t print a prompt */
emit_prompt = 0; /* handy for automatic testing */
/* Install the signal handlers */
/* These are the ones you will need to implement */
Signal(SIGINT, sigint_handler); /* ctrl-c */
Signal(SIGTSTP, sigtstp_handler); /* ctrl-z */
Signal(SIGCHLD, sigchld_handler); /* Terminated or stopped child */
/* This one provides a clean way to kill the shell */
Signal(SIGQUIT, sigquit_handler);
/* Initialize the job list */
initjobs(jobs);
/* Have a user log into the shell */
username = login();
/* Execute the shell’s read/eval loop */
while (1) {
/* Read command line */
if (emit_prompt) {
printf(“%s”, prompt);
fflush(stdout);
if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
app_error(“fgets error”);
if (feof(stdin)) { /* End of file (ctrl-d) */
fflush(stdout);
/* Evaluate the command line */
eval(cmdline);
fflush(stdout);
fflush(stdout);
exit(0); /* control never reaches here */
* login – Performs user authentication for the shell
* See specificaiton for how this function should act
* This function returns a string of the username that is logged in
char * login() {
return NULL;
* eval – Evaluate the command line that the user has just typed in
* If the user has requested a built-in command (quit, jobs, bg or fg)
* then execute it immediately. Otherwise, fork a child process and
* run the job in the context of the child. If the job is running in
* the foreground, wait for it to terminate and then return. Note:
* each child process must have a unique process group ID so that our
* background children don’t receive SIGINT (SIGTSTP) from the kernel
* when we type ctrl-c (ctrl-z) at the keyboard.
void eval(char *cmdline)
* parseline – Parse the command line and build the argv array.
* Characters enclosed in single quotes are treated as a single
* argument. Return true if the user has requested a BG job, false if
* the user has requested a FG job.
int parseline(const char *cmdline, char **argv)
static char array[MAXLINE]; /* holds local copy of command line */
char *buf = array; /* ptr that traverses command line */
char *delim; /* points to first space delimiter */
int argc; /* number of args */
int bg; /* background job? */
strcpy(buf, cmdline);
buf[strlen(buf)-1] = ‘ ‘; /* replace trailing ‘\n’ with space */
while (*buf && (*buf == ‘ ‘)) /* ignore leading spaces */
/* Build the argv list */
if (*buf == ‘\”) {
delim = strchr(buf, ‘\”);
delim = strchr(buf, ‘ ‘);
while (delim) {
argv[argc++] = buf;
*delim = ‘\0’;
buf = delim + 1;
while (*buf && (*buf == ‘ ‘)) /* ignore spaces */
if (*buf == ‘\”) {
delim = strchr(buf, ‘\”);
delim = strchr(buf, ‘ ‘);
argv[argc] = NULL;
if (argc == 0) /* ignore blank line */
/* should the job run in the background? */
if ((bg = (*argv[argc-1] == ‘&’)) != 0) {
argv[–argc] = NULL;
return bg;
* builtin_cmd – If the user has typed a built-in command then execute
* it immediately.
int builtin_cmd(char **argv)
return 0; /* not a builtin command */
* do_bgfg – Execute the builtin bg and fg commands
void do_bgfg(char **argv)
* waitfg – Block until process pid is no longer the foreground process
void waitfg(pid_t pid)
/*****************
* Signal handlers
*****************/
* sigchld_handler – The kernel sends a SIGCHLD to the shell whenever
* a child job terminates (becomes a zombie), or stops because it
* received a SIGSTOP or SIGTSTP signal. The handler reaps all
* available zombie children, but doesn’t wait for any other
* currently running children to terminate.
void sigchld_handler(int sig)
* sigint_handler – The kernel sends a SIGINT to the shell whenver the
* user types ctrl-c at the keyboard. Catch it and send it along
* to the foreground job.
void sigint_handler(int sig)
* sigtstp_handler – The kernel sends a SIGTSTP to the shell whenever
* the user types ctrl-z at the keyboard. Catch it and suspend the
* foreground job by sending it a SIGTSTP.
void sigtstp_handler(int sig)
/*********************
* End signal handlers
*********************/
/***********************************************
* Helper routines that manipulate the job list
**********************************************/
/* clearjob – Clear the entries in a job struct */
void clearjob(struct job_t *job) {
job->pid = 0;
job->jid = 0;
job->state = UNDEF;
job->cmdline[0] = ‘\0’;
/* initjobs – Initialize the job list */
void initjobs(struct job_t *jobs) {
for (i = 0; i < MAXJOBS; i++)
clearjob(&jobs[i]);
/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
int i, max=0;
for (i = 0; i < MAXJOBS; i++)
if (jobs[i].jid > max)
max = jobs[i].jid;
return max;
/* addjob – Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
if (pid < 1)
for (i = 0; i < MAXJOBS; i++) {
if (jobs[i].pid == 0) {
jobs[i].pid = pid;
jobs[i].state = state;
jobs[i].jid = nextjid++;
if (nextjid > MAXJOBS)
nextjid = 1;
strcpy(jobs[i].cmdline, cmdline);
if(verbose){
printf(“Added job [%d] %d %s\n”, jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
printf(“Tried to create too many jobs\n”);
/* deletejob – Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
if (pid < 1) for (i = 0; i < MAXJOBS; i++) { if (jobs[i].pid == pid) { clearjob(&jobs[i]); nextjid = maxjid(jobs)+1; /* fgpid - Return PID of current foreground job, 0 if no such job */ pid_t fgpid(struct job_t *jobs) { for (i = 0; i < MAXJOBS; i++) if (jobs[i].state == FG) return jobs[i].pid; /* getjobpid - Find a job (by PID) on the job list */ struct job_t *getjobpid(struct job_t *jobs, pid_t pid) { if (pid < 1) return NULL; for (i = 0; i < MAXJOBS; i++) if (jobs[i].pid == pid) return &jobs[i]; return NULL; /* getjobjid - Find a job (by JID) on the job list */ struct job_t *getjobjid(struct job_t *jobs, int jid) if (jid < 1) return NULL; for (i = 0; i < MAXJOBS; i++) if (jobs[i].jid == jid) return &jobs[i]; return NULL; /* pid2jid - Map process ID to job ID */ int pid2jid(pid_t pid) if (pid < 1) for (i = 0; i < MAXJOBS; i++) if (jobs[i].pid == pid) { return jobs[i].jid; /* listjobs - Print the job list */ void listjobs(struct job_t *jobs) for (i = 0; i < MAXJOBS; i++) { if (jobs[i].pid != 0) { printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid); switch (jobs[i].state) { printf("Running "); printf("Foreground "); printf("Stopped "); printf("listjobs: Internal error: job[%d].state=%d ", i, jobs[i].state); printf("%s", jobs[i].cmdline); /****************************** * end job list helper routines ******************************/ /*********************** * Other helper routines ***********************/ * usage - print a help message void usage(void) printf("Usage: shell [-hvp]\n"); printf(" -h print this message\n"); printf(" -v print additional diagnostic information\n"); printf(" -p do not emit a command prompt\n"); * unix_error - unix-style error routine void unix_error(char *msg) fprintf(stdout, "%s: %s\n", msg, strerror(errno)); * app_error - application-style error routine void app_error(char *msg) fprintf(stdout, "%s\n", msg); * Signal - wrapper for the sigaction function handler_t *Signal(int signum, handler_t *handler) struct sigaction action, old_action; action.sa_handler = handler; sigemptyset(&action.sa_mask); /* block sigs of type being handled */ action.sa_flags = SA_RESTART; /* restart syscalls if possible */ if (sigaction(signum, &action, &old_action) < 0) unix_error("Signal error"); return (old_action.sa_handler); * sigquit_handler - The driver program can gracefully terminate the * child shell by sending it a SIGQUIT signal. void sigquit_handler(int sig) printf("Terminating after receipt of SIGQUIT signal\n");